What is causing the ozone layer to get smaller?

Chloroflorocarbons (CFCs) did. From what i've heard the ozone layer is starting to slowly heal up again.

According to a report (2011) by the Scientific Assessment Panel of the U.N. Montreal Protocol on Substances that Deplete the Ozone Layer, the ozone layer has, over the last decade, reached a turnaround point. It is no longer decreasing, but it is not yet increasing.